Poly(ethylene terephthalate) articles and method

ABSTRACT

Disclosed is a process of making an oriented and heat set blow molded bottle of poly(ethylene terephthalate) so that the bottles resulting from the process have a density over 1.3860 cc./gm. and an onset-of-shrinkage temperature over 80° C. In the process preform preheated to a temperature suitable for orientation is biaxially stretched in a blow mold and then while the hollow article walls are still in contact with the blow mold walls, the article is raised to a higher heat setting temperature in the range of 200°-250° C. (except for the neck) thus heat setting the bottle, and while the article is still at a shrinkage resisting pressure exceeding atmospheric cooling the article to a temperature at which it maintains its shape when not pressurized but not below 100° C. It is also particularly disclosed that this cooling step can be done outside the mold. In a special embodiment of the invention where the cooling step is effected outside the mold, the cooling under the shrinkage resisting pressure is below 100° C., even down to room temperature and lower, before the shrinkage resisting pressure is released from the hollow article.

This is a division of application Ser. No. 354,473 filed Mar. 3, l982.

This invention relates to improved methods of making hollow, biaxiallyoriented, heat set partially crystalline articles. In another aspect itrelates to biaxially oriented, heat set hollow poly(ethyleneterephthalate) articles having a density of over 1.3860 and lowpermeabilities to carbon dioxide and oxygen gases, and also having ahigh "onset-of-shrinkage" temperature compared with hollow articles heatset according to prior art processes.

In order to improve several physical properties of hollow articles suchas bottles made from poly(ethylene terephthalate), it has been suggestedthat biaxially oriented poly(ethylene terephthalate) hollow articles,made by orientation blow molding of a preform or parison underconditions to provide biaxial orientation and concomitantcrystallization, be further heat treated at higher temperatures than theorientation blowing temperature to further increase the density (orcrystallinity) of the hollow article. Such increasing of the density orcrystallinity by heating after shaping under orientation conditions iscommonly known as heat setting.

Wyeth et al. in U.S. Pat. No. 3,733,309 suggests such a process.However, the heat setting process is mentioned only in passing and nospecific examples including heat setting are present in the patent. Ofcourse, the extra step would ordinarily add considerable expense to thebottle making process.

Collins in U.S. Pat. No. 4,039,641 discloses heat setting containers ofan organic crystallizable synthetic thermoplastic polymeric material.Among such materials disclosed are high density polyethylene,polypropylene homopolymers and copolymers and polyesters such aspoly(ethylene terephthalate) and poly(butylene terephthalate), includingcopolyesters such as ethylene terephthalate/isophthalate copolymers. Ina preferred embodiment, heat setting is accomplished by blowing theplastic parison in a heated blow mold, preheated to the heat settingtemperature.

It is stated in Collins that the heat setting temperature used is thatnormally encountered in heat setting of oriented films or fibers madefrom the given plastic material. It is not stated, however, what heatsetting temperatures are "normal" for making oriented films or fibersfrom poly(ethylene terephthalate). See Collins, infra. However, for thisplastic it is disclosed in Collins that the mold is preferablymaintained at 130° to 220° C.

It is disclosed in Collins that after heat setting, the container shouldbe cooled down to a temperature, for instance, below about 60° C. In oneexample of Collins, the heat setting temperature of the mold is 200° C.and in the other, it is 140° C.

In unexamined Japanese patent application No. 146,175, laid open Nov.15, 1980, containers are stretch blow molded under conditions tobiaxially orient the polyester molecules. It is explained that as aresult of the stretch blow molding, the residual strain was large andthat when heated subsequent to the molding, the residual strain wasreleased, causing deformation of the container. To solve this problem,the reference recommends heat setting the containers after blow molding.It is also recommended that the heat setting temperature in unstretchedareas such as the neck be held to 95°-125° C. so that hazing will notoccur in these areas. Other areas are heat set at a higher temperature.It is recommended that the heat setting of the highly strained areas ofthe container be in the range from 125° C. to 235° C. However, quenchingof the heat set container at 100° C. or above is not disclosed.

Unexamined Japanese patent application No. 77,672, laid open June 21,1979, is similar except that it is not taught to heat set unorientedparts at a lower temperature than other parts. The highest temperaturedisclosed for heat setting is 130° C. and in the only specific examplethe oriented blow molded bottle is heat set by contacting with the hotblow mold kept at 130° C. and then lowering the mold temperature to 100°C. to prevent bottle deformation when the bottle is discharged from themold. In this reference, it is stated that hazing occurs when higherheat setting mold temperatures are used. The reference does not disclosethe present method or the novel products of the present invention.

In unexamined Japanese patent application No. 21,463, laid open Feb. 17,1979, a blown poly(ethylene terephthalate) bottle was heat set byheating the bottle to 140° C. while still within the blow mold.

In unexamined Japanese patent application No. 78,267, laid open June 11,1978, there is disclosed stretch blow molding a thermoplastic resin, inthe example specifically poly(ethylene terephthalate) to make a hollowarticle, and while the article is still in the mold to introduce hotgases for purposes of heat setting. In the example, the hot gas is at180° C. The example does not disclose cooling the heat set articlebefore removal from the mold, but the description of the drawing doesdescribe this as an alternative treatment, using normal temperaturecompressed gas to cool the molded piece.

In unexamined Japanese patent application No. 66,968, laid open May 29,1979, methods of reducing residual strain in biaxially oriented blownbottles are disclosed. The methods are applied to unidentified,saturated polyester resins. In all of the methods the bottle is heated,after being formed by biaxial orientation blow molding by one method oranother. After the heat treatment the bottle is cooled, but thetemperature to which the bottle is cooled is not disclosed. The heatingstep apparently includes heating the neck portion of the bottle, sincein one method the heating is by passing steam through channels 8 whichinclude channels 8 next to the neck, and in another method heating iscarried out by high temperature pressurization of the interior of thebottle, which of course includes the neck.

In unexamined Japanese patent application No. 78,268, laid open June 11,1978, a stretch blow molded hollow body, including those made frompoly(ethylene terephthalate) is heat set by introducing hot gas underpressure into the interior of the bottle while in the mold. After theheat setting, normal temperature gas can be optionally blown into thearticle to cool the article before removal from the mold, or the heatset body can simply be exhausted to atmospheric. In an example, theheated gas for heat setting is at 200° C. In the specific example, nocooling before removal from the mold was disclosed. Again, the heatingincludes heating of the neck portion of the bottle.

In unexamined Japanese patent application No. 41,973, laid open Apr. 3,1979, it is disclosed to heat set stretch blow molded containers,including those made from poly(ethylene terephthalate) by heating theblown containers at a high temperature and then rapidly cooling them toroom temperature. Heat treatment can be within the mold while underpressure and the heating can be by means of a hot mold. It is disclosedthat the heat treatment should be such that the density of the bottlebody following the heat treatment is no greater than 1.40 gms./cc. Inthe example given, steam at 179° C. is used for heating the mold in theheating step.

Scarlett No. 2,823,421 discloses heat setting of PET films using heatsetting temperatures of 150°-250° C. after orientation stretching. Thispatent does not state, however, what "normal" PET film heat settingtemperatures are. It does disclose that for a film stretched three timesin each direction that a heat setting temperature of 200° C. ispreferred by Scarlett.

German No. 2,540,930 discloses heat setting of hollow articles. Theblank or parison is blow molded at 70°-140° C. and then cooled in themold to below 70° C. Thereafter, the bottle can be reheated to heatsetting temperature in that mold or in a different mold. The heatsetting temperature is said to be over 140° C. or higher. In thedisclosed process the entire bottle including the neck is heated in theheat setting step to the same temperature and the neck of the bottlecrystallizes to an opaque state.

In Brady et al. No. 4,233,022 a bottle oriented by blow molding PET at75°-100° C. is heat set. Heat setting is accomplished in a hot mold at asuitable heat setting temperature; examples of such temperatures aregiven as 150° to 220° C. The patent features controlling different zonesof the bottle at different temperatures, so that all the sidewall of thebottle is at the maximum heat setting temperatures being used, but thefinish or neck, for instance, is actually cooled to preventcrystallization thereof. In this patent after the heat setting step, itis stated that the bottle is cooled to a selfsustaining condition.

In one embodiment the present process features biaxially orienting aparison preheated to orientation temperature, by inflating in a blowmold which has been preheated to the higher, heat setting temperatureand holding the bottle or other hollow article against the mold wall forthe short time necessary to effect heat setting. The process of thepresent invention also features thereafter cooling the heat set hollowarticle or bottle while under pressure but not below 100° C. and thenexhausting the pressure in the bottle to essentially atmospheric orambient pressure before further cooling of the article below 100° C.takes place.

The prior art merely discloses that the bottle needs to be cooled to aself-sustaining condition or it discloses that it must be cooled to somespecific temperature which is obviously very low and at which suchbottles are self-sustaining.

For instance, Collins No. 4,039,641 specifically discloses cooling tobelow 60° C. and in one specific example cools to 40° C., beforereleasing the gas pressure.

I have found that the "onset-of shrinkage" temperature for the heat setsidewall of the poly(ethylene terephthalate) hollow articles orcontainers of the invention depends on the density of the sidewall andthe temperature to which the hollow article is cooled before theinflating pressure of the article is exhausted to essentiallyatmospheric pressure.

The onset-of-shrinkage temperature referred to herein was determined asdescribed in Brady and Jabarin "Thermal Treatment of Cold-FormedPoly(Vinyl Chloride) Polymer Engineering and Science", pp. 686-90 ofVol. 17, No. 9, September 1977, except that the samples were cut fromthe sidewalls of the bottles. No thermal treatment was effected on thecut samples prior to the tests.

Ordinarily, when a PET bottle is blown in a blow mold, it is cooled toquite a low temperature, a temperature very much below the temperatureat which the bottle would be self-sustaining, in fact much below thetemperature at which the bottle will shrink at all when the pressure isreleased. According to an important feature of the present invention, Icool the heat set bottle, while still under pressure preventingshrinkage, to a temperature which will allow the volume of the hollowarticle to shrink no more than 6 percent, preferably 5 percent, when thepressure is removed and allowed to cool to room temperature, but nolower than 100° C., before releasing the pressure to equalize it withthe ambient atmosphere. I have discovered that cooling under pressure,i.e. when not allowing shrinkage, below 100° C. progressively reducesthe onset-of-shrinkage temperature even when the final room temperaturevolume remains the same and does not decrease with decreasing "quench"temperature. Thus, referring to the tables described hereafter, it willbe seen that the volume remains essentially constant for quenchtemperatures of 90° C. and below but that the onset-of-shrinkagetemperature becomes progressively lower. It has also been found that thetrend continues above 100° C. quench temperature, i.e. that theonset-of-shrinkage temperature increases as the quench temperatureincreases above 100° C.

One advantage of the present process is that a great decrease in cycletime is obtained in my heat setting process over processes disclosed orsuggested in the prior art, because the bottle is left in a mold onlyfor the time necessary to cool it to the relatively high temperaturerange before indicated, so that the next cycle can be immediatelystarted; or the bottle can be immediately removed from the mold in oneembodiment without cooling.

The process of the present invention, as well as the product, isconcerned with polymers of poly(ethylene terephthalate) having aninherent viscosity of at least 0.6. Poly(ethylene terephthalate)polymers useful in the present invention includes

polymers where at least 97% of the polymer contains the repeatingethylene terephthalate units of the formula: ##STR1## with the remainderbeing minor amounts of ester-forming components, and

copolymers of ethylene terephthalate wherein up to about 10 mole percentof the copolymer is prepared from the monomer units selected frombutane-1,4-diol; diethylene glycol; propane-1,3-diol; polytetramethylene glycol); poly ethylene glycol); poly(propylene glycol);1,4-hydroxymethylcyclohexane and the like, substituted for the glycolmoiety in the preparation of the copolymer, or isophthalic; naphthalene1,4- or 2,6-dicarboxylic; adipic; sebacic; decane-1,10-dicarboxylicacids, and the like, substituted for up to 10 mole percent of the acidmoiety (terephthalic acid) in the preparation of the copolymer.

Of course, the poly(ethylene terephthalate) polymer can include variousadditives that do not adversely affect the polymer. For instance, somesuch additives are stabilizers, e.g., antioxidants or ultraviolet lightscreening agents, extrusion aids, additives designed to make the polymermore degradable or combustible, and dyes or pigments. Moreover,cross-linking or branching agents such as are disclosed in U.S. Pat. No.4,188,357 can be included in small amounts in order to increase the meltstrength of the poly(ethylene terephthalate).

It is an object of the present invention to provide an improvedmanipulative process for producing poly(ethylene terephthalate) hollowarticles which are biaxially oriented, heat set and highly crystallineas indicated by density, which process results in a maximum efficiencyof production.

It is another object of the present invention to provide a process forproducing a poly(ethylene terephthalate) hollow article having superioroxygen and carbon dioxide permeability properties and having increasedthermal stability (high onset-of-shrinkage temperature). It is a furtherobject to provide such poly(ethylene terephthalate) hollow articleshaving a combination of such superior properties never before disclosedin the art. The highly crystalline nature of such new products and thepermeability properties are directly related to their density, so thatthe new products of the present invention have high densities andconsequently low permeabilities coupled with higher onset-of-shrinkagetemperatures not known in the prior art for heat set poly(ethyleneterephthalate) hollow articles.

Other objects, as well as aspects and advantages, of the presentinvention will become apparent from a study of the specification.

In one of its broadest aspects the process of the invention comprises

(1) biaxially orienting the body of a hollow article by blow molding ahollow poly(ethylene terephthalate) preform preheated to a suitableorientation temperature range,

(2) while said article is still under pressure sufficient to maintainits essential size and shape, heating to a higher temperature in therange 200° to 250° C. the portions thereof that it is desired tocrystallize, thereby increasing the density of such portions, and

(3) while said article is still under a pressure sufficient to maintainits essential size and shape, cooling said article to a temperature atwhich it maintains its shape even without internal pressure aboveatmospheric but not below 100° C., and

(4) thereafter exhausting the pressure from the hollow article at saidtemperature and allowing the article to cool further while not underinternal pressure. Steps (3) and (4) result in a heat set article havinga higher "onset-of-shrinkage" temperature than if all cooling orquenching be done under pressure down to ambient temperature.

According to an important aspect of the present invention I haveprovided a method of making a high density, partially crystalline,biaxially oriented hollow poly(ethylene terephthalate) plastic articlehaving a neck or finish portion comprising

(1) enclosing a tubular parison of said poly(ethylene terephthalate),having a closed end and an open end destined to form the neck or finishof the hollow article, within a blow mold, which parison is at a firsttemperature range, which first temperature range is conducive toorientation during stretching,

(2) while said parison is still at said first temperature rangeexpanding said parison into contact and conformance with the blow moldwalls by inflation with a gas under pressure to make a hollow blownarticle, said stretching and expanding under the resulting strainconditions resulting in biaxial orientation and concomitant partialcrystallization, and then while the article walls are still inflated incontact with said mold walls, raising the temperature of the article toa higher second temperature in the range 200° to 250° C., except for theneck or finish portion of said article which is kept at a lowtemperature such that crystallization is minimized or eliminated so thatthe neck or finish portion remains transparent; this temperature isusually in the range of 40°-125° C., more usually 40°-80° C., but anynon-crystallizing temperature of 125° C. or below can be used,

(3) wherein the heating in said second temperature range heat sets thebody of said article by causing further crystallization thereof asindicated by density increase,

(4) and while said hollow article is still at a shrinkage-resistingpressure exceeding atmospheric, cooling said article to a temperature atwhich it maintains its shape when not pressurized but not below 100° C.,and

(5) thereafter reducing the gas pressure within said article toessentially ambient pressure.

According to another aspect of the present invention, there is providednew a product which is the product of the foregoing process: atransparent hollow article of poly(ethylene terephthalate) having aninherent viscosity of at least 0.6 dl/gm., the body portion of saidarticle being biaxially oriented and heat set and having a density over1.3860 gm./cc. and an onset-of-shrinkage temperature of over 80° C.

In a preferred embodiment of the present process the heat setting secondtemperature is in the range of 225° to 250° C. The product of thispreferred process is a transparent hollow article of poly(ethyleneterephthalate) having an inherent viscosity of at least 0.6 dl./gm., thebody portion of said article being biaxially oriented and heat set andhaving a density over 1.3930 gm./cc. and an onset-of-shrinkagetemperature of over 105° C.

Thus, the present process of orientation blow molding and heat settingnot only produces articles with increased density (crystallinity), withthe known decrease in oxygen and carbon dioxide permeabilities but italso has the following advantages over the prior art:

(1) increased productivity rate because of decreased cycle time,

(2) compared to prior art heat set PET bottles, higheronset-of-shrinkage temperatures, important for hot-fill packaging offluid products, and

(3) energy savings because of lack of necessity to repeatedly cool themold to low temperatures each cycle.

FIGS. 1, 2 and 3 are each the same view looking at the flat side ofone-half of a split blow mold, each showing the hollow plastic invarious stages. Thus, in FIG. 1 the parison 1 is shown after it isenclosed in the two halves of the split blow mold but before any airpressure has been applied. FIG. 2 shows parison 1 extended by the blowpin and FIG. 3 shows the completely blown bottle 2.

The apparatus shown in the drawings and the description of its operationherein are suitable for effecting the process of, and making the productof, the present invention, and were used in the specific examplesdiscussed hereafter. However, other specific blow molding apparatus canof course be used to effect the orientation blow molding at onetemperture, heat setting at a higher temperature and subsequent coolingunder shrinkage-resisting pressure to a desired temperature according tothe invention and, finally, the exhausting of the internal pressure fromthe hollow article.

In the drawings, 3 is body of the blow mold (i.e., one-half thereof),made up of neck ring 4, lower section 6 and upper section 7. Sections 6and 7 are mostly separated by air gap 8 to minimize heat conductiontherebetween and 6 and 7 are in physical contact only at narrow annularband 9. Lines 11 and 12 are provided for introducing cooling water intoand from, respectively, channels (not shown) in 6. Lines 13 and 14 areprovided for introducing cooling water into and from, respectively, neckring 4 (one of the split halves of which is depicted in the figures).Lines 16 and 17 are for introducing oil for heating or cooling the mold,as the case may be, into and from the mold, respectively. Each of 11, 13and 16 are connected to an appropriate source (not shown) of fluid underpressure.

Electric resistance strip heater 18 encircles the bottom of section 7and is used to help make up for loss of heat flowing vertically fromsection 7 to section 6.

Blow mandrel 19 is shown inserted in parison 1; the blowing air isintroduced into parison 1 via line 27 through cylinder 21 andpassageways (not shown) in the end of mandrel 19, and the samepassageways serve for exhaustion of air from the blown article. Cylinder21 contains a mechanism which includes a piston (not shown) that has anO-ring that forms a seal against the top of the mandrel duringoperation. Stretch rod 22 is vertically movable through 21 and 19 bymeans not shown.

In operation a preheated injection molded parison 1 is enclosed in thesplit blow mold as shown in FIG. 1 and the mandrel is inserted. Theupward progress of stretch rod 22 is begun a split second beforeintroduction of blowing air through mandrel 19 and then the blowing airis introduced to blow the bottle against the walls of the mold. Thestretch rod during initial blowing arrives at the position shown in FIG.2 and is retracted before the blowing air is evacuated. The neck orfinish area during the entire process is kept cool by the circulatingcool water flowing through the halves of upper mold sections 6 and neckring halves 4. During the orientation blowing and heat setting step,section 7 is maintained at the desired heat setting temperature bycirculating hot oil through 16, 7 and 17 and by heating the lower partof section 7 with resistance heater 18.

While FIG. 2 shows parison 1 elongated without any increase in the hoopdirection, undoubtedly 1 is actually partly inflated before it reachesthe position shown in FIG. 2, so that axial mechanical stretching andpneumatic inflation are occurring together. Although my apparatus wasrun as described here and as described in connection with the examples,it is equally possible (1) to complete the axial mechanical stretchingbefore beginning pneumatic inflation, or, on the other hand, (2) not touse any mechanical axial stretching with the stretch rod at all; indeed,many commercial biaxially oriented bottles are made by blow moldingwithout the use of any mechanical axial stretching.

In the drawings 23 and 24 are thermocouples positioned as shown and 1/8inch from the mold cavity wall. In extensive testing, it was shown thatthe temperature varied only about 4° to 5° F. between the twothermocouples with the hottest temperature being at 23 near the bottomof the bottle.

After heat setting for the desired time, the hot oil is displaced by acontinuous flow of room temperature oil to cool the bottle to thedesired "quench" temperature as determined by the average of the twothermocouple temperatures. Then the pressure is released and the moldopened.

In the apparatus described a series of bottles of the shape shown inFIG. 3 were blown under biaxial orientation conditions, heat set bycontact with the hot mold and quenched to the temperature indicated inTables 1 and 2. Then the pressure was released and the mold was opened.In two minutes each bottle, after release of the pressure, was filledwith room temperature water and the volume measured by measuring thewater used. Unless noted otherwise, each bottle was made frompoly(ethylene terephthalate) having an inherent viscosity of 0.72dl./gm. Various properties were obtained as indicated in the tables.

For comparison or control purposes, a bottle was blown identically tothe others except that it was blown into a cold mold and cooled to 23°C. Thus, the control had no heat setting but was only biaxially orientedand not heat set, during the course of which its density increased to1.3634 gms./cc. Its onset-of-shrinkage temperature was 46° C.

The bottles in the examples represented by the data in Tables 1 and 2were made from injection molded parisons having the general shape shownin FIG. 1. They were 4 inches long with a wall thickness of 145-150 milsand weighed 26 gms. The parisons were preheated to about 190° F.(outside surface 190° F., inside surface 188° F.). The parison at thistemperature was enclosed in the split halves of the blow mold, one-halfof which is shown in FIG. 1. Then the stretch rod 22 was pushed againstthe bottom of the parison for 0.15 second before the blow pressure airwas applied at 100 psig for 0.5 second, after which it was increased to300 psig, and the stretch rod was maintained in the position shown onFIG. 2 for 2 seconds and was then retracted. At all times cold watercirculated through lower mold section 6 and neck ring 4 so that theunexpanded neck was kept cold. The blown bottle is of course blownagainst the blow mold wall, which is maintained at the heat settingtemperature shown in Table 1 or 2 for the time shown in the table. Afterthis time, cold oil was circulated to replace the hot oil for the lengthof time needed to lower the temperature to the quench temperature shownin the tables. Once this temperature was reached, the bottle wasexhausted to atmospheric and the mold was opened. The bottles arethereafter allowed to cool, eventually to room temperature, withoutinternal pressure.

In the examples summarized in Tables 1 and 2, the bottles were allwell-shaped unless indicated as "deformed". Also, the nominal overflowvolume of the bottles with no shrinkage is about 522 cc.

                  TABLE 1                                                         ______________________________________                                        Heat                        Volume     Onset                                  Setting  Quench    Density.sup.(1)                                                                        2 min..sup.(2)                                                                       24 hrs.                                                                             Temp.                                °C.                                                                         Sec.    Temp. °C.                                                                        gm./cc.                                                                              cubic centimeters                                                                        °C.                           ______________________________________                                        250  30      148       1.4013                                                 250  120     148       1.4022                                                 240  6       180       1.3980 497.9  497.4                                    240  6       170       1.3980 501.9  501.6                                    240  6       160       1.3980 506.2  506.1 184                                240  6       150       1.3980 509.3  509.2                                    240  6       130       1.3978 513.9  514   172                                240  6       120       1.3978 516.1  515.9 168                                240  6       110       1.3978 518.5  518.4 --                                 240  6       100       1.3965 519.4  519.7 154                                240  6        90       1.3970 520.8  520.9 143                                240  6        80       1.3986 521.7  521.7 139                                240  6        80       1.3982 none.sup.(3)                                                                         521.8 --                                 240  6        60       1.3982 521.8  522.1 132                                230  6       170       1.3950 493.1  493.6 --                                 230  6       160       1.3950 499.5  498.8 168                                230  6       150       1.3950 504.1  503.8 --                                 230  6       140       1.3950 509.0  508.6                                    230  6       129       1.3950 512    511.6 148                                230  6       124       1.3947 514.1  513.7 138                                230  6       100       1.3947 520.7  519.8 120                                230  6        85       1.3945 521.1  520.6 113                                230  6        75       1.3945 521.4  520.9 104                                230  6        60       1.3950 521.8  521.8  88                                ______________________________________                                         .sup.(1) at midsidewall                                                       .sup.(2) overflow volume measured by filling with room temperature water      minutes after opening mold.                                                   .sup.(3) allowed to cool 24 hours in air without filling with water until     then.                                                                    

                                      TABLE 2                                     __________________________________________________________________________    Heat              Volume                                                      Setting                                                                              Quench                                                                              Density.sup.(1)                                                                    2 min..sup.(2)                                                                     24 hrs.                                                                           Onset                                              °C.                                                                       Sec.                                                                              Temp. °C.                                                                    gm./cc.                                                                            cubic centimeters                                                                      Temp. °C.                                   __________________________________________________________________________    220                                                                              6   160   1.3912                                                                             Deformed                                                    220                                                                              6   150   1.3928                                                                             500.9                                                                              500.7                                                  220                                                                              6   140   1.3910                                                                             502.9                                                                              502.9                                                  220                                                                              6   135   1.3912                                                                             506.0                                                                              505.8                                                                             114                                                220                                                                              6   120   1.3914                                                                             513.9                                                                              513.6                                                                             108                                                220                                                                              6   110   1.3918                                                                             517.5                                                                              517.4                                                                             100                                                220                                                                              6   100   1.3918                                                                             519.8                                                                              519.5                                                                             94                                                 220                                                                              6    90   1.3923                                                                             520.5                                                                              520.5                                                                             88                                                 220                                                                              6    80   1.3919                                                                             521.2                                                                              521.4                                                                             83                                                 220                                                                              6    60   1.3922                                                                             521.5                                                                              521.5                                                                             76                                                 200                                                                              6   140   1.3867                                                                             Deformed                                                    200                                                                              6   130   1.3867                                                                             496.5                                                                              495.7                                                                             102                                                200                                                                              6   115   1.3868                                                                             513.0                                                                              513.0                                                                             95                                                 200                                                                              6   100   1.3877                                                                             519.9                                                                              519.8                                                                             84                                                 200                                                                              6    90   1.3870                                                                             519.9                                                                              520.0                                                                             80                                                 200                                                                              6    80   1.3860                                                                             520.8                                                                              520.4                                                                             78                                                 200                                                                              6    60   1.3872                                                                             521.0                                                                              520.8                                                                             74                                                 130                                                                              6   100   1.3702                                                                             509  508.4                                                                             74    (Deformed)                                   130                                                                              120 100   1.3744                                                                             512.2                                                                              511.7                                                                             74    (Deformed                                    __________________________________________________________________________     .sup.(1) at midsidewall                                                       .sup.(2) overflow volume measured by filling with room temperature water      minutes after opening mold                                                    .sup.(3) allowed to cool 24 hours in air without filling with water until     then.                                                                    

The last two examples are a repetition of the example in Jap. No.77,672, infra. The bottles were misshapen, i.e., they were completelyout of round, and of course, they have lower onset temperatures and thedensities are lower than the products of the invention.

The bottles made at 250° C. heat setting temperature were made of 0.9inherent viscosity PET.

From the results shown in Tables 1 and 2 it will be seen that I havediscovered, surprisingly, that the onset-of-shrinkage temperature (for agiven density oriented and heat set hollow article) becomes lower as thequench temperature becomes lower, even when the volume stays constant.Thus, I have discovered that higher quench temperatures, where thequenching takes place while the hollow article is restrained againstshrinkage, gives higher onset-of-shrinkage temperatures.

In Table 3 are shown results of tests for the permeation of oxygen andof carbon dioxide for one-half liter bottles made according to theinvention.

The determination procedures were as follows:

Carbon dioxide barrier properties of containers were determined by a gaschromatographic method. Containers were placed in a test fixture inwhich carbon dioxide gas at one atmosphere absolute was established andmaintained at the outside surface and dry nitrogen gas at one atmosphereabsolute at the inside surface. Carbon dioxide permeates through thewall from the outside to the inside of the container. The nitrogen gasinside the container was periodically sampled for permeated carbondioxide with a gas chromatograph. The rate of carbon dioxide permeationwas determined from the rate of increase of CO₂ concentration in thenitrogen gas inside the container. The system was calibrated by using anassayed calibrating gas of CO₂ in nitrogen supplied by Matheson GasProducts. Carbon dioxide test gas was moisturized to 50-100% relativehumidity in the test fixture by evaporation of water from severalsponges. Test temperature was controlled by placing the entire apparatusin a closed room which was controlled at 73 ±2° F.

A method employing a Hersch coulometric detector was used to determineoxygen barrier properties of containers. The apparatus is similar to anOxtran 100 Permeation Analyzer manufactured by Modern Controls, ElkRiver, Minn. A test fixture was used to establish oxygen and nitrogengases at one atmosphere absolute at the outside and inside surfaces ofthe container respectively. Oxygen surrounding the outside surface wascontinuously replaced by a flowing gas stream which was vented to theatmospheric environment. The nitrogen gas inside the container was alsoa flowing system and served as a sweep gas. Oxygen permeated through thewall from the outside to the inside of the container where it was pickedup by the nitrogen sweep gas and carried to the coulometric detector formeasurement and venting to atmosphere. The output of the detector isdirectly proportional to the amount of oxygen it receives andcalibration is computed from well established laws of electrochemistry.Both oxygen and nitrogen gases were moisturized by bubbling throughtubes of water prior to entering the test fixture. Test temperature wascontrolled by placing the apparatus in a closed room which wasmaintained at 73 ±2° F.

The results in the following Table 3 are for nominal one-half literbottles made from parisons each weighing about 25.85 grams and made asdescribed for the bottles in connnection with Tables 1 and 2. Thecontrol bottles were merely blown under orientation conditions as beforedescribed and quenched to near room temperature without heat settingwhile the heat set bottles were heat set at 241° C. as indicated.

                  TABLE 3                                                         ______________________________________                                        Heat-Set                                                                             Quench   Oxygen      Carbon Dioxide                                    Temper-                                                                              Temper-  Permeation  Permeation                                                                              Density                                 ature °C.                                                                     ature °C.                                                                       (cc/day atm)                                                                              (cc/day atm)                                                                            gms./cc.                                ______________________________________                                        control         0.126       0.830     1.3630                                  control         0.128       0.760     1.3630                                  control         0.125       --                                                control         0.125       --                                                average         0.126       0.795                                             241    147      0.093       0.498     1.3996                                  241    148      0.087       --                                                241    147      0.089       0.499     1.4000                                  241    147      0.090       --                                                average         0.090       0.498                                             Average Improvement                                                                       29%         37%                                                   ______________________________________                                    

The results illustrate the magnitude of the recognized improvement inthe oxygen and carbon dioxide barrier properties of PET with increaseddensity obtained by heat setting.

In an especially advantageous embodiment of the process of the inventionthe heat set hollow article is removed from the mold at heat-settingtemperature and is cooled outside of the heat setting mold to thetemperature of 100° C. or higher before designated prior to equalizingthe internal pressure of the hollow article with the ambient atmosphere.After heat setting the pressure is reduced to a pressure which maintainsits volume about the same as when within the mold, the mold is opened,and the bottle is cooled without confinement in a mold. This cooling cansimply be air cooling in the room temperature air. When the desiredquench temperature of 100° C. or higher is reached, the internalpressure is then released before further cooling. This specific processoffers the shortest cycle time since no blow mold time is spent forquenching; it also results in the greatest energy savings since the blowmold can be kept at constant temperature.

The data for the 1/2 liter bottles shown in Table 4 was obtained usingthis embodiment of my process. The process was effected exactly asdescribed in connection with the discussion of Tables 1 and 2, exceptmodified as described in the previous two paragraphs herein. Thepressure to which the bottles were adjusted and automatically heldduring the quench step is as shown. The cooling of the bottles to the"quench" temperature took place outside the mold with the outsidesurface thereof unrestrained so that the bottles simply cooled in theambient room temperature air. The temperatures were estimated ratherclosely but are not exact.

                  TABLE 4                                                         ______________________________________                                                Quench                                                                Heat Setting                                                                            Press  Temp.    Density                                                                              Volume Onset                                 °C.                                                                          Sec.    Psig   °C.                                                                           gms./cc.                                                                             ccs.   Temp.                               ______________________________________                                        230   6       23     170    1.3950 491    163                                 230   6       23     115    1.3950 515    127                                 ______________________________________                                    

If one modifies this last embodiment of my invention--wherein the hollowarticle is removed under some pressure from the mold at heat settingtemperature--so that the article outside the heat setting mold isallowed to cool under shrinkage-resisting pressure to below 100° C., aslow as room temperature, e.g. 20° C., or even lower, the maximum benefitof higher onset-of-shrinkage temperatures is not realized, but theadvantages of minimum cycle time and the energy savings still obtain.Accordingly, the invention includes this special embodiment; usually onecools to below 80° C., often below 70° C., before exhausting the air orother gas from the hollow article.

Thus, in many instances the higher onset-of-shrinkage temperatureobtained when cooling to no lower than 100° C. before releasing theshrinkage resisting pressure, as in the principal embodiment of theinvention, is not necessary for the particular end use of the hollowarticle.

To illustrate this last embodiment, a bottle was made in the same manneras in the 230° C. bottles summarized in Table 4 except that the heatsetting temperature was 240° C. and the pressure was 17 psig and thispressure was not released until the bottle had cooled to about 70° C. inthe ambient atmosphere. Its density was 1.3975 gms./cc., the bottlevolume was 520.5 cc. and the onset-of-shrinkage temperature was 149° C.

When inherent viscosity is referred to herein, it is the viscosity asmeasured in a 60/40 weight ratio phenol/tetrachloroethane solution at25° C. Density was determined by the method described in ASTM 1505,entitled "Density Gradient Technique".

As will be evident to those skilled in the art, various modifications ofthis invention can be made or followed in the light of the foregoingdisclosure and discussion without departing from the spirit and scope ofthe disclosure or from the scope of the claims.

I claim:
 1. A transparent hollow article of poly(ethylene terephthalate)having an inherent viscosity of at least 0.6 dl./gm., the body portionof said article being biaxially oriented and heat set and having adensity over 1.392 g/cc and a volume shrinkage of less than about 6%. 2.A transparent hollow article of poly(ethylene terephthalate) having aninherent viscosity of at least 0.72 dl./gm., the body portion of saidarticle being biaxially oriented and heat set and having a density over1.392 g/cc and a volume shrinkage of less than about 5%.
 3. An articleas defined in claim 2 in which the density of the heat set sidewall isover about 1.393 g/cc.
 4. A transparent hollow article or orientedpolyethylene terephthalate that is heat set and that has an onset ofshrinkage temperature of at least about 105° C. and a shrinkage of lessthan about 5% of the volume, the article being a hollow container with abody including an oriented sidewall, the oriented sidewall being heattreated to increase the density thereof to at least about 1.392 g/cc byheating to a temperature equivalent to a temperature of about 220° C. to250° C., the heat treated sidewall being quenched while under ashrinkage reducing pressure to provide the article with a shrinkage ofless than about 5% of the volume and an onset of shrinkage temperatureof at least about 105° C., the quenching being done at a temperatureequivalent to that of about room temperature to 170° C. at a high heatsetting temperature of 240° C., about 80° C. to 160° C. for a heatsetting temperature of about 230° C., and about 120° C. to 140° C. for alower heat setting temperature of about 220° C.
 5. An article as definedin claim 4 in which the sidewall is heat set at about 230° C. andquenched at about 100° C.
 6. An article as defined in claim 4 in whichthe sidewall is heat set at about 240° C. and quenched at about 180° C.